The present invention relates generally to mechanical cotton pickers. More particularly, the present invention relates to rotary doffer assemblies of improved advantageous construction for removal of cotton from rotating picking spindles in conventional machines for cotton picking.
Typical cotton picker units include rotating heads disposed on a vertical axis and carrying a series of radially extending rotating spindles which pick exposed cotton from open cotton bolls as a consequence of the rotation of the spindles on their own axes and by reason of slight barbing or roughening of the spindle surfaces. In turn, the cotton-bearing spindles pass rotating doffer discs having radially extending and vertically projected annular teeth or lugs which function to wipe or doff the gathered cotton from the spindles as the doffers and spindles rotate in cooperating relationship. The operation of conventional picking units and the arrangement of doffers and spindles are described and depicted in Deere and Company publication No. A-29-84-1 "Cotton Pickers and Strippers" which is incorporated herein by reference.
In operation, the picker spindles of cotton machines not only are subjected to varying accumulations of cotton thereon depending upon increases or decreases in the harvested yield per acre, relative moisture content of the bolls, variations in speed at which the field is traversed, and the like, but likewise, encounter varying accumulations of associated matter such as rocks, dirt, plant stock, weeds, etc. Accordingly, the lugs or teeth of the doffer assemblies as well as the associated hub and disc to which the doffer lugs are attached are subjected to varying load stresses, shock forces and elevated temperatures during normal operation which tend to cause splitting and breakage of the doffer elements or otherwise sufficient wear and deterioration to require the expensive replacement of individual doffer elements and, depending upon the degree of difficulty encountered in picker-doffer alignment, may necessitate the replacement of the entire doffer assembly.
Heretofore, various doffer designs have been suggested to provide doffers which are sufficiently flexible to accomodate the abrasion, shock, and friction load forces and temperatures to which the doffer assemblies are subjected while at the same time attempting to maintain sufficient structural rigidity to promote adequate wear life for such doffer assemblies. For example, doffer elements, including the annular lugs thereon, made of an elastomeric material such as sponge rubber are disclosed in U.S. Pat. No. 2,738,636. U.S. Pat. No. 2,693,071 discloses doffer discs in which the disc body is derived from thermosetting or thermoplastic materials and the doffing fingers or lugs are produced from tire tread stock. It has been found through field experience that such doffer elements derived from elastomeric rubbers, while providing the desired resiliency, do not maintain sufficient durability levels and are further disadvantageous from the standpoint that such normally black materials when subjected to the load stresses and temperatures encountered during operation tend to result in black specks in the raw cotton which often objectionably appear in the final cotton fabrics.
Another approach is that of U.S. Pat. No. 2,847,815 describing doffer lugs or pads which are integrally connected to a center disc made of rubber or synthetic rubber material having a Durometer hardness of 60 and in which the disc is strengthened by the inclusion of fabric rings, e.g., cotton, artificial fibers such as nylon, rayon or dacron bonded to both sides of the disc.
More recently, U.S. Pat. No. 3,971,197 describes doffer elements comprising an integrally molded doffer with a disc shaped reinforcement, preferably perforated, embedded in the doffer along a rim or annular portion of the disc. The doffer body is of molded elastomeric material such as natural or synthetic rubbers and blends thereof or may be derived from liquid cast materials such as polyurethane. The polyurethane material is described only as being capable of liquid casting or molding and having a Durometer range of 70-90 on the shore A hardness scale. The doffer assembly described may also be constructed with layers of polyurethane so that the first layer may comprise 10 to 30% of the doffer thickness and have a Durometer of 55-75 on the shore D hardness scale while a second layer is 70 to 90% of the thickness having a hardness range of 65 to 95 on the shore A hardness scale. The foregoing doffer allows for both circumferential and axial deflection.
However, it has been found in practice that the doffers derived from such castable polyurethanes, while achieving a degree of flexibility are, nevertheless, subject to deterioration through breakage of the doffer lugs or large portions thereof when subjected to shock and striking forces such as those resulting from the doffer elements being struck by accumulated debris between the spindles and the doffer elements or by striking of the lugs by the rotating spindles if minor misalignments should occur.